CORRELATION BETWEEN MODULATION NOISE AND UNIAXIAL ANISOTROPY IN HIGH COERCIVITY THIN-FILM RECORDING MEDIA

Modulation noise, arising from the zigzag domain patterns in the magnetization transition regions of thin film metallic recording media, represents one of the major problems and limitations in the application of these media for high-density digital recording. It is generally accepted that this type of noise arises primarily from the exchange coupling between the crystallites of the media. In the recent literature, we find several attempts to correlate this noise with some magnetic property of the media, such as the rotational hysteresis integral (Rh) or the coercive squareness (S), but such correlations apply only under special conditions. In this investigation, we studied the recording and noise characteristics of many different high-coercivity thin film media and their total magnetic anisotropy measured by a torque magnetometer. We found a good correlation between the in-plane anisotropy and the media noise and pulse width of the media. In the presence of high in-plane anisotropy, magnetization reversal in the transition regions must take place essentially in the plane, resulting in zigzag domains and wider transition lengths. A lower in-plane anisotropy allows for magnetization reversal to proceed in part out of the film plane, reducing the length of the transition regions and zigzag noise. Thus, torque magnetometry is a very useful means of characterizing and optimizing thin film media. © 1990 IEEE